Econometric models of demand are useful tools for studying the impact of key factors on current and future demand. The demand for medical care is conceptually similar to the demand for other goods and services. Models of the demand for medical care have been built, but no previous work has been done on the demand for rheumatologist care. The overall goal of this proposed study is to build two econometric models of the demand for outpatient rheumatologist care by using cross-sectional primary data collected from patients and rheumatologists. The four specific aims of this project are to: 1) construct and pilot test four survey instruments designed to collect relevant data from rheumatology patients and physicians; 2) recruit a geographically and organizationally diverse sample of 24 rheumatologists, collect data from them and from all patients seen in each of their practices during a one week time-period, and then follow these patients prospectively for a year; 3) construct two econometric regression models using these primary data to analyze the demand for rheumatology office visits and the demand for total out-patient charges for rheumatologic care; and 4) perform a series of sensitivity analyses to estimate how changes in the explanatory variables affect the demand for outpatient rheumatology visits and charges. The models will be built on data from approximately 1500 subjects with various rheumatic diseases. The explanatory variables in the models will include: disease factors such as diagnosis, functional status, and pain; sociodemographic factors such as age, sex and education; and economic factors such as income, health insurance, and medical care price. This study is significant in several ways. It will identify the degree to which specific factors influence the demand for rheumatologist care; it will be the first study to specifically examine the demand function for cognitive, outpatient services; it will explicitly incorporate a number of important clinical variables that are generally absent from econometric models; and it will firmly establish a new focus for the E/E/HSR Component of this Arthritis Center.